Refrigeration apparatus and method employing



Jan. 5, 1954 N. M. WARMON 2,664,715

REFRIGERATION APPARATUS AND METHOD EMPLOYING COLD ACCUMULATOR Filed Feb.26, 1949 /I x/ xx INVENTOR.

ka WT F/VEY Patented Jan. 5, 1954 ath ne UNITED STA'EES PATENT OEFEEREFRIGERATION APPARATUS AND METHOD EMPLOYING COLD ACCUMULATOR NilsMagnus Warmon, Stockholm, Sweden, as-

signor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation ofSweden 10 Claims.

My invention relates to refrigeration, and more particularly topreservation of frozen food packages and the like and freezing of foodspreparatory to storage and preservation thereof.

It is an object of my invention to provide an improvement in'efrigerators for storing frozen food packages and the like and freezingfoocls to prepare them for such storage and preservation, which isparticularly suited for refrigerators of this type operated bycontinuous absorption refrgeration systems employing an inert gas orpressure equalizing agent, whereby a maximum amount of useful storagespace is made available for a refrigerator of a given size. I accomplishthis by providing cold accumulators containing a suitable eutecticsolution which may be placed in the storage space of a refrigerator ofthis type during periods of light or normal load, the eutectc solutionin such cold accumulators freezing during such Operating periods andserving as a source of refrgeration which supplements the refrigeratingeffect produced by the refrigeration system of the refrigerator duringperiods of increased load, as when pachages containing food to be frozenare placed in the storage space, for example.

The above and other objects and advantages of this invention will bebetter understood from the following description and accompanyingdrawing forming a part of this specification, and of which:

Fig. 1 is a front vertical section more or less diagrammaticallyillustrating a refrigerator einbodying the invention;

Fig. 2 is a side vertical section of the refrigerator shown in Fig. l toillustrate details more clearly;

Fig. 3 is a front vertical section of a refrigerater diagrammaticallyillustrating another embodinent of the invention; and

Figs. 4 and 5 are front and side elevations of a part employed in therefrigerators of Figs. 1 to 3 inclusive.

Referring to Figs. 1 and 2, the invention is shown in connection with arefrigerator comprising a cabinet I@ having an inner metal shell iiarranged to be supported within an outer metal shell 2 and insulatedtherefrom with any suitable insulating material i i. The inner metalshell !i defines a thermally insulated storage space 95 for storingfrozen food packages iii and also holding packages il containing food tobe .frozern as will be described presently. Access to the storage space[5 is had through the open top thereof which is adapted to be closed bya removable closure member or lid !8 containing a suitable insulatingmaterial.

The storage space !5 is arranged to be cooled by an evaporator !9 in theform of a coil which is disposed about the inner metal shell and in goodthermal contact therewith, as by welding. The evaporator is is connectedto a condenser ZE! which is in heat exchange relation with a coolingelement Zi, the evaporator li) and condenser 28 forming a secondary heattransfer system in which the evaporator is of the fiooded type and at alower level than the condenser.

The evaporator 59 and condenser 26) form a closed fluid circuit which ispartly filled with a suitable volatile fluid that evaporates in theevaporator [9 and takes up heat thereby producing cold. The vapor fiowsfrom evaporator iii into condenser 2!) in which the vapor is cooled andcondensed by cooling element 2 i. The liquid condensate formed incondenser 29 returns by gravity through Conduit 22 to the evaporator !8.

The cooling element 2! forms part of a refrigeration system of theabsorption type containing an inert gas or pressure equalizing agent. Insuch a system refrigerant vapor is expelled from absorption liquid in aboiler 23 by heating and flows through a conduit 24 to an air cooledcondenser 25. The refrigerant vapor, such as arnmonia, is liquefied inthe condenser 25 and fiows through conduit 26 into cooling element Zi inwhich liquid refrigerant evaporates and diifuses into an inert gas, suchas hydrogen, to produce a refrigerating effect for condensing vapor inthe condenser 20.

The resulting gas mixture of refrigerant and inert gas fiows fromcooling element 2! through a Conduit 21 and one passage of a gas heatexchanger 28 to an absorber which may be of an air cooled type includinga coil and an absorber vessel. In the absorber refrigerant is absorbedfrom the gas mixture into absorption liquid, such as water, which isdelivered thereto. The inert gas is returned from the absorber to thelower end of cooling element Zi through another passage of gas heatexchanger 28, and absorption liq uid enriched in refrigerant fiows fromthe absorber to the boiler 23 in which refrigerant vapor is expelledfrom liquid. Absorption liquid deprved of refrigerant returns from theboiler 23 to the absorber to absorb refrigerant vapor, such circulationof liquid usually being effected by vapor-liquid lift action. In orderto simplify the drawing, the boiler 23 is schematically illus tratedwhile the absorber and connections thereof to other elements of therefrigeration system 3 have net been shown, such parts being well knownand their iliustration not being necessary for an understandin of myinvention.

In accordanoe with the invention I provide cold accunulators E@containing a suitable eutectic solution which 'may be placed in thestorage space !5 during periods of light or normal load on theabsorption refrigeration system, thereby causing the eutectic solutionto freeze and serve as a source of refrigeration which supplements thererigerating efiect produced by the absorption refrigeration systemduring periods of increased load. In this way the cold accumulatorsbecome "charged during periods of light or normal load, that is, areconditioned to serve as a supplementary source of 'cold which isadvantageously utilized to take care of socalled peai loads, as when anumber of packages containing food to be frozen are placed in thestorage space i at practically the same time.

As best shown in Figs. i and 5, the cold accumulators Sii comprisesubstantially flat sheets i and 32 which are relatively close to oneanother, the peripheral edge portions of the sheet 3! being fiangedperipheral edge portions of the sheet 32, as indicated at 33. Fhe spacedapart sheets 32 and 32 may be iormed of galvanized iron sheeting or anyother suitable material, and the joint therebetween may be brazed orsoldered to provide a liquid tight seal. In order that the coldaccumulators 39 will stand up under continued use, the outer 'surfacesthereof may be coated with a layer of corrosion resisting material, suchas an asphalt lacquer, for example.

An end Wall of the cold accumulators 39 desirably is formed with twothreaded openings adapted to receive threaded caps or closure members Si and respectively, one of which serves as a filling opening for asuitable eutectic solution and the other as a vent for Venting air fromthe interier of the cold accumulator When it is being filled withthesolution. The closure members sa and 35 should effectively seal theeutectic solution within the interior of the cold accumulators 3& andmay be shaped so that the latter can be raised and readily moved Withthe aid of a suitable tool or clamp having parts adapted to take hold ofthe closure members and readily removable therefrom.

In the refrigerator ill illustrated in Figs. l and 2, frozen foodpackages !3 positioned in the storage space !5 are stacked upon oneanother in several rows adjacent opposing side walls and an end wall ofthe inner metal shell or liner i i. At the opposite end of the storagespace !5 are positioned a number of cold accumulators 30 which serve asa supplementary source of cold and cooperate with the refrigerat'ng eectproduced by the absorption refrigeration system to eect freezing of foodwithin the packages H. In Figs. i and 2, a cold accumulator 30 ishorizontally positioned directly on the bottom of the inner metal shellH. Each package !1 is positioned between adjacent horizontally disposedcold accumulators, so that heat will be rapidly taken up by the coldaccumulators from opposite sides of each package at the same time,thereby promoting quick freezing of oods which is desirable in certaininstances in order that the physical characteristics of the food willnot be impaired.

In accord with the the invention the cold accumulators 353 are placed inthe storage space !5 when space is available and the load in therefrigerator is normal. By a normal load is meant bent back andoverlying the outwardly a load which is made up primarily of frozen foodpackages which are already at a low temperature. Under such conditionsthe load on the refri erator is relatively light because therefrigeration then required must only be sufficient to balance the heatleakage of the refrigerator cabinet. When the cold accumulators 30 areplaced in the storage space 15 to be conditioned for use, they may beplaced horizontally on top of one'another without any insertstherebetween, or in upright positions adjacent to one another so thatair can circulate therebetween. The greater the surface contact isbetween the inner metal shell ii and the cold accumulators, the lesstime Will then be required to condition the cold accumuiators ready foruse in the manner previously described and shown in Figo. l and 2.

Another manner of employing the cold accumulators E@ to effect quickfreezing of packaged food is shown in Fig. 3 which illustrates arerigerator like that shown in Figs. 1 and 2, like parts 'beingdesignated by the same reference numerals. In Fig. 3 the packagcs llcontaining food to be frozen are positioned vertically betweenvertically disposed cold accumulators 3%, one of which bears directlyagainst a side Wall of the inner metal shell i i. While in Figs. 1 and 2the weight of the aceumulators themselves insures a good thermal contactbetween the latter and the packages il, this is not so in thearrangement of Fig. 3. Accordingly, provision must be made to cause thecold accumulators to bear against the opposing sides of the verticallydisposed packages. This may be accornplished by providing a suitablyshaped clamp 35 which acts to hold a group of assembled coldaccumulators and packages resiliently together, thereby snugly holdingthe accumulators against the sides of the packages.

It is especially desirable to employ in the cold accumulators 3& aneutectic solution possessing corrosion resisting properties, and I havefound that sodium nitrite and potassium chromate, and in certaininstances sodium chromate, have such desirable properties. In employingsodium nitrite to provide an eutectic solution, I have found that anaqueous solution of sodium nitrite with a dehydrated salt content ofabout 397% by weight has a freezing temperature or eutectic point ofabout -15.5 C. In employing potassium chromate to provide an eutecticsolution, I have found that an aqueous solution of potassium chromatewith a dehydrated salt content of about 355% by weight has a freezingtemperature or eutectic point of about -l1.4 C., and a melting heat ofabout 49 to 50 kcaL/kg. In employing sodium chromate to provide aneutectic solution, I have found that an aqueous solution oi` such a salthas a reezing temperature or eutectic point of about -5 C.

It is desirable to employ an eutectic solution whose freezing andmelting temperature is more or less constant and is not subject toexcessive undercooling or supercooling. stated another way, the freezingtemperature of eutectic solutions often varies and such solutions oftenactually freeze at a temperature which is below the temperature at whichreezing actually should take place. When this occurs, it may be saidthat the eutectic solution is "undercooled or "supercooledi' While theaqueous solution of sodium nitrite referred to above possesses corrosionresisting properties, it frequently freezes at a temperature of -23 C.although its eutectic point is in the neighborhood of -15 C. The

is admirably suited for use as an eutectic solution.

When the temperature of the refrigerator storage space is 'maintained ata temperature in the neighborhood of -16 C., the undercooling of 'aneutectic solution of potassium -chromate has been found to be about 4 C.Hence, the maxiimum variation in freezing temperature of the aqueoussolution of potassium chromate which can be expected is relatively smalland in a range of only 4 C., while such variation in freezingtemperature of the aqueous solution of sodium nitrite is greater 'and ina range of about 8 C Since the freezing temperature or eutectic point ofthe -aqueous solution of sodium chromate is in the neighborhood of -5C., such an eutectic solution is not satisfactory to effect rapidfreezing of food since the freezing temperature of most foods is about-2 C., and this difference in temperature is not sufiicient.

The length of time required to freeze food is more or less in inverseratio to the difference in temperature of the freezing point of foodsand the temperature of the surfaces of the cold accumulators when theeutectic solution therein is frozen and conditioned for use. In order toinsure freezing of the eutectic solution employed in the coldaccumulators 3!) at all times, and disregarding undercooling orvariations in freezing temperature of the eutectic solution whichpossibly may occur, the freezing temperature of the eutectic solutiondesirably should be at least 3 to 4 C. above the temperature at whichthe freezing space of the refrigerator is normally maintained, and lessthan C., preferably in a temperature range of about -10 to -17 C.

When the storage spaces of the refrigerators shown in the drawing aremaintained at a normal Operating temperature of about -16 C. by theabsorption refrigeration system employing an inert gas, it will be seenthat cold accumulators se containing an eutectic solution of potassiumchromate like that referred to above Satisfactorily meet theserequirements. The eutectic point of the aqueous solution of potassiumchromate being about -11.4 C., such eutectic point is about 4.6` C.above the temperature at which the storage space is normally maintainedand also falls below -10 C. and in the temperature range of .-10 to -17C.

When the cold `accumulators 30 are charged with a suitable eutecticsolution, the accumulators should not be completely filled with liquidbecause the eutectic solution expands to a considerable extent uponfreezing. When the cold accumulators 30 are vertically disposed in themanner shown in Fig. 3, the air pockets therein are at the extreme upperregions and will not impair the effectiveness of the cold accumulatorsbecause the frozen mass is in good contact with both of the opposingsurfaces 31 and 32.

However, when the cold accumulators 30 are horizontally disposed in themanner shown in Figs. 1 'and 2, air pockets in 'parts thereof which bearagainst packages containing food tobe frozen is not desirable. In suchcase, provision should be made in any suitable manner to provide an airpocket which will not impair the usefulness of the cold :accumulators toeifect rapid freezing of foods. However, even when the cold accumulators3!! are to be used in the manner shown in Figs. 1 and 2, suchaccumulators may be conditioned for use by placing them vertically inthe storage space l5.

In view of the foregoing, it will now 'be evident that by employing coldaccumulators 3@ like those illustrated and just described, -arefrigerator adapted to -operate at a sufciently low temperature forstoring frozen food packages and freezing foods prior to storage may beof minimum size to take care of a definite maximum load. This isespecially true when a refrigerator employed as a freezer is maintainedat a low temperature with an absorption refrigeration system of theinert gas type which operates continuously and hence differs fromcompression refrigeration systems which only operate a part of the time,such intermittent Operating interval of time depending upon thecharacter of the load, that is, whether only frozen food `packages 'arebeing kept at a safe refrigerating temperature to prevent thawingthereof, or such a load is supplemented by a load required to freezefood contained in Dackages or wrapped in 'any other manner.

since the very character of absorption refrigeration systems of theinert gas type lena themselves to continuous operation, the provision ofcold accumulators 30 is admirably suited for refrigerators particularlyconstructed for freezing purposes which are operated by inert gasabsorption refrigeration systems. By way of example and withoutlimitation, it is only necessary to provide a refrigerating or coolingeifect of about 50 kcaL/hr. in a freezer space of about 3 cubic feet fora normal or light load primarily consisting of frozen food packageswhich are already at a low temperature, and in such case therefrigerating effect necessary must only be suicient to balance the heatleakage of the refrigerator cabinet, as previously explaned.Accordingly, a freezing unit of minimum size` may be employed in accordwith the invention when a continuously Operating absorption refrigeration system of the inert gas type is employed which meets the minimumrequirements for such a normal or light load and maintains the thermallyinsulated storage space at a temperature in a range of -l2 to -20 C.When the load on the refrigerator increases above the normal or lightload the cold accumulators, previously conditioned for use, can beefifectively employed to provide an additional or supplementary source;f refrigeration to take care of such additional oad.

Modifications of the embodiment of my invention which I have describedwill occur to those skilled in the art, so that I desire my inventionnot to be limited to the particular arrangements set forth. For example,a corrosion resisting agent may be added to an eutectic solution as wellas employ an eutectic solution formed of salts which in themselvespossess corrosion resisting properties, as described above. Therefore, Iintend in the claims to cover all those modifications which do notdepart from the spirit and scope of my invention.

What is claimed is:

In a method of refrigeraticn, the steps which comprise artificiallyproducing a refrigerating efiect by a refrigeration system at a place ofcooling which is disposed exteriorly of a thermally insulated space andin thermal relation therewith to maintain such space at a desired lowtemperature to preserve matter therein below the freezing temperature ofwater when the load in said space is in a first range, positioning oneor more readily movable bodies of eutectic

